Motor control system



.M w Km 55 N Q Ma m .0 Am m Original Filed Oct. ll, 1 953 2 Sheets-Sheet 1 Inventor 2 Le 59 J onid A. Urn

His ttorney.

Reiseued May 4,1937

PATENT OFFICE .Mo'ron CONTROL SYSTEM Leonid A. Umanslry, Schenectady, N. Y., assignor to General Electric Company, a corporation oi New York Original No. 2,021,757,

Serial No. -693,138, October 11,

dated, November 19, 1935,

1933. Application for reissue December 8, 1936, Serial No.

25 Claims.

This invention relates to control systems, more particularly to systems in which an object is control systems for electric motors, and a more specific object is the provision of means for controlling the input to the controlled motor in accordance with the rate of change of speed of a control element.

In another of its aspects, the invention relates to motor control systems for apparatus having a motor driven element-operating on. a strip of material and a motor driven reel for supplying .the strip to the operating element or taking up the strip delivered by the operating element, and a further object of the invention is the provision 20"bf means for maintaining a substantially'constant an element operating on a strip of material 'andtension in the strip between the operating element and the reel during acceleration and deceleration of the driving motors as well-as when the motors are operating at constant speed. 1

In carrying the invention into efiect in one form thereof, the energization ,of a dynamo-electric machine is varied in accordance with the speed of a variable speed controlling element and this. machine is provided with a substantial amount of fly-wheel effect so that its current varies in accordance with the rate of change'of speed of the controlling element and this variable current'is utilized to exert a controlling action on the device or object which it is desired to control.

As applied to the control 0! motors for driving the supply or take-up reels, a regulator is provided for maintaining substantially constant current input to the reel motor while operating at constant speed; and means responsive to the rate oi change of speed of the element driving motor are provided for varying the setting of the regu- 'lator in proportion tothe rate of change of speed substantial fly-wheel eflect so that it draws a cur-' of the element driving motor. In one'embodiment the rate of 1 change of speed responsive means for varying the regulator setting takes the form of an additional coil on the regulator for modifying'theaction of the regular operating coil,

together with a dynamo-electric machine-connected in circuit with the additional regulator .coi1,- supplied with a voltage varying with the speed of the operating element, andde'signed with rent varying with the rate'of change of speed of the element driving motor to vary the setting of the regulator.

In illustrating the invention-in one form there- 'of it is shown as embodied in a motor control system for the mill and take-up reel motors of a cold strip steel rolling mill. more complete understanding of the invention reference should now be had to the following specification and to the accompanying drawings in which Fig. l is a simple, diagrammatical representation of an embodiment of the invention and Figs. 2and 3 are simple diagrammatic representations of modifications thereof.

Referring now to the drawings, a strip of material i0 such for example ascold steel is being fed in the direction of the arrow to a pair of reducing rolls ll between which the gauge of the strip is suitably reduced and the strip emerging from the rolls is wound upon'a take-up reel I2. The rolls ii are driven by any suitable driving means illustrated in the drawings as an electric motor i3 of the direct current type which in turn is supplied from any suitable source such as that represented by the variable voltage generator ll, with the armature of which the armature of the motori3 is connected in a loop circuit when the switch I5 is-in its closed position. Similarly the For a better and reel i2 is driven by'a direct current driving mosuitable driving means (not shown) such for exv ample as a synchronous motor or an alternatin currentinduction motor. As shown, the generator ll is provided with a field winding i8 supplied from a suitable constant potential source represented by the plus and minus supply lines a 2G and its excitation is adjusted by means of a suitable rheostat 2i included in circuit therewith. As is well understood, operation of the rheostat- 2| to vary the excitation of, the field i8 produces a corresponding variation in the voltage of the generator I4 and the speed of the driving motors l3 and I5 supplied therefrom. ,The connection of a driving motor in a loop circuit with a variable voltage generator, such as shown in the drawings, is usually referred to in the art as a Ward-Leonard connection and it has the advantage that the speed of the motor can be. smoothly v included in the circuit of the fly-wheel' motor and the auxiliary coil 35 for making minor adjustments without changing the fly-wheel.-

For different settings of the regulator setting rheostat 28, the same amount of accelerating current in the armature of the reel motor will vary the eii'ect of the regulator operating coil 25 and thus it becomes necessary to change the effect of the auxiliary coil 35 in proportion. For this purpose a rheostat II is provided which shunts a larger or smaller proportion of the current drawn by the fly-wheel motor 33. As shown, this rheostat is mechanically coupled to the regulator setting rheostat 28 and is operated by a common hand wheel so that it varies the efiect of the auxiliary coil 35 in proportion to 'the amount the regulator setting rheostat 23 varies the effect of the coil 25 during acceleration and deceleration of the reel.

The operation of the system is as follows:

Assuming that the supply generator II is being driven at its proper speed, the mill motor l3 and the reel motor it are started from rest by operating the rheostat 2| to decrease the resistance in the field circuit of the supply generator and thus to increase the generator voltage. For the pass in which the motor I5 driving the reel to wind the delivered strip, the movable contact of switch 3| is moved to engage its upper stationary contact, thereby rendering the regulator contacts 30 active so that the regulator responds to regulate the motoring action. For any given mill speed, the fly-wheel motor 33 operates at a corresponding speed and draws an almost insignificant current from the tachometer generator 32.

As long as the mill speed remains constant, the regulator 25 functions in the previously described manner to maintain substantially constant current input to the reel motor 16 by increasing the excitation of the reel motor to decrease the speed thereoi as the diameter of the coil on the reel l2 increases. Thus, for any mill speed the regulator 25 maintains substantially constant tension in the strip between the reel and the mill rolls. a

If new the speed oi the mill is increasedthe voltage of the pilot generator 32 in proportion,and the fly-wheel motor 33, tending to iollow the speed of the pilot generator 32 will draw an increased current in order to accelerate its armature and the ily-wheel 31. This rate oi change of speed of the'mill motor which in the illustrated system serves as the" current is approximately proportional to the rat oi change of speed of the pilot generator 32 and is thus approximately proportional to variablespeed controlling element. Thus the value of the current drawn by the fly-wheel motor serves as a measure of the rate '1 change 01 speed of the mill. Since this current flows through the auxiliary coil 35 which at this time is acting diflerentially with respect to the operating coil 26, the eflect is automatically to increase the "setting of the regulator without tampering-with its operating coil 25 or its cir cuit. The greater the acceleration of the mill, the greater will be the bucking action of the auxiliary coil 35 and thus the higher will be setting oi the regulator. In other words, the in-. creased current flowing in the auxiliary coil 35 decreases'the eil'ect of the operating coil 23 and this allows the reel motor l to draw the increased current that is necessary in order to accelerate its own armature and the mass of the reel without decreasing or losing the tension in will increase the the strip between the reel and the mill rolls. Thus, it will be seen that the setting of the regulator is automatically and properly adjusted to allow the reel motor to.draw .the current required for acceleration. As the fly-wheel motor comes up to speed, the acceleration gradually decreases and thus the regulator 25 gradually returns-to its original setting.

When the mill is decelerated by decreasing the 'voltage of the supply generator I, the direction of the current flowing in the circuit of the flywheel motor and the auxiliary coil 35 will reverse. This is due to the fact that the fly-wheel is an energy storagedevice and gives up its stored energy in the form oi electric current when the voltage of the pilot generator is decreased below the value of the counter voltage of the fiy-wheel motor 33. As a result the effect of the auxiliary coil 35 and the operating coil becomes cumulative thereby decreasing the efl'ective setting of the regulator, which condition is exactly what is required for decelerating the reel motor so as not to rupture the strip or unduly increase its tension.

It will thus be seen that substantially constant tension is maintained in the strip between the mill rolls and the reel not only during constant speed operation of the mill but during periodsof acceleration and deceleration as well.

In the above description it has been assumed that the reel l2 1 operating as a take-up reel. However, if the mil is a reversing type mill, during the succeeding pass, thereel operates as a supply reel, and the motor operates as a drag generator driven by the strip, returning energy to the system and maintaining back tension in the strip between the reel and the mill. For this operation, the movable contact of the switch 3| is moved into engagement with its stationary contact-thereby rendering the back contacts 30s of the regulator active to control the resistance 24. The result of this change is to cause the regulator to respond .to "generating" this connection it is to be noted that when the /contacts 33 are'active an increase in the armature current causes the contacts fll to short-circuit the resistance 24 and thereby strengthen the field. This is the correct regulating action if the regulated machine is operating as a motor. It the contacts III. are active, an increase in the armature current causes the contacts 30;. to

open, insertthe resistance 24in the field circuit and thereby weaken the fleld,,which is the correct regulating, actionv ii the regulated machine is operating as a generator.- The operation of the fly-wheel dynamo-electric machine 33 under this condition is similar, but the reverse of that just described for the preceding pass. Thus .the terms take-up reel" and motor" are to be understood as employed in a descriptive and not in a limiting sense. I

c The arrangement shown in the modification of Fig. 2 is in most respects identical with the system: of Fig. 1. However, mi this modification a variable rheostat I4 is included in the field circuit oi the mill motor 45 so controlled not only by the generator voltage, but also by weakening the field of the mill motor. As shown, the motor field rheostat 44 is mechanically connected to the rheostat 45 in the field action. In

that the mill speed is not supplied from a l\ the system of Fig. l.

ening until after the generator'has been brought to full voltage.

In this modification the fly-wheel motor II is pilot generator as in the system of Fig. 1 but on the other hand is connected directly across the mains of the supply generator There is a definite advantage in connecting the armature of the fly-wheel motor 5.0 across the terminals of the supply generator instead of energizing it from a separate pilot generator as in the system or Fig.1. It isobvious' that the generator voltage increases before the mill speed can follow the increase of voltage. Therefore, the

regulator forcing coil 5i will be energized slightly earlier than would be the case it the fiy-wheel motor were connected to a pilot machine. This anticipating action is especially advantageous means, such ior will cause the fly-wheel able accelerating. current when starting up from rest.

After the mill and reel have-been accelerated by raising the generator voltage, the rolling speed may be further increased by weakening the field oi the mill motor 45. Obviously, any suitable to the rheostat 44 and actuated by the handwheel ll may be utilized to weaken the field of the fly-wheel motor 53 simultaneously with the weakening of \the field of the mill motor. This machine to draw a suitfrom the generator mains; this current, fiowing through the forcing coil 5| will suitably increase the setting 01" the regulator and willpermit the reel motorto maintain the strip tension substantially constant even during this part or the accelerating period.

The operation of the modified systemoi Fig. 2 is otherwise substantially identical with the previously described operationfor the system of Fig. 1 and repetition is unnecessary.

In the modified system shown in Fig. 3 the fivwheel motor Bil is supplied from a pilot generator 8! driven by the mill motor 82 as in the system of Fig. l. The regulator 81 is in all respects identical with the regulator 25 in Fig. 1. The

modified system of Figs3 is diflerent from the practically nil.

system of Fig. 1 in that the armature or a booster generator. is included inthe armature circuit or the reel motor between the armature terminals of the latter andthe mainsoi the supply generator '6. is driven at a speed which is preferably substan.- tially constant by any suitable driving means illustrated as an alternating current motor 31 supplied iroma suitable source indicated by the three supply lines I. EitherXasynchronous motor or an induction motor may be utilized to drive the generator N. Asshown.the field winding 10 is included in the circuit oi the armature of the fiy-wheel motor Cl and the auxiliary regulator coil.

In operation, when the mill is operating at substantially constant speed, the running light current 0! the fiy-wheel motor is practically negligible, with the result that the excitation and generated voltage of the booster generator 04 are Asthespeedofthemillisincreased by increasing the voltage or thesupply example as a rheostat similar The booster generator 64' generator I, the fly-wheel motor 6|) draws a current proportional to the rate of change of speed of the mill. This increased current flowing through the fieldwinding' lil oi! the booster generator will cause the latter to generate and introduce an additional voltage in the armature circuit or the reelmotor 65. This additional voltage introduced in the armature circuit of the reel motor will cause the latter to accelerate without any tendency to diminish the strip tension. It is also evident that the polarity of the booster generator is automatically reversed so that it becomes a bucking generator during deceleration andassists the reel motor to decelerate properly without any tendency to increase the tension.

In other words, in the arrangement shown in Fig. 3, the additional input to the reel motor, required either wholly or partly by temporarily increasing the applied voltage, instead of obtainingthis additional input entirely by increasing the armature current as in Figs. 1 and 2. In an extreme case, a properly designed booster generator 64, may fully take care of maintaining tension during acceleration and retardation, dispensing entirely with the forcing coil on the regulator 63. The remainder of the arrangement and its operation /isin all respects will not be repeated. In accordance with the provisions of the patent statutes this invention is described as embodied in concrete form but it will be understood that the apparatus, elements, and connections shown and described are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to personsskilled in the art without departing from the true spirit of this invention and the scope of the annexed claims.

What I claimas new and desire to secure by Letters Patent 01' the United States, is: a

1. In combination, a variable speed element; means for supplying a voltage varying with the speed of saidelement, a dynamo-electric machine connected to said supply-means and provided with substantial fly-wheel effect so that its current varies with the rate of change of speed or said element. 2. In a control system a variable speed element, control means, and means for actuating said control means comprising a dynamo-electric machine provided with substantial fiy-wheel effect and means for supplying a voltage varying. with the speed of said element to said machine so that oi said element.

3. A control system comprising a variable speed during the accelerating period, is obtained identical with that of Fig. 1 and element, a controlled object, a control device for said object, and means for actuatingsaid device comprising a dynamo-electric machine provided with substantial fiy-wheel effect and means for supplying a voltage varying with the'speed of I I said elementto said machine so that its current varies with the rate of change 5: speed 01' said element.

4. A control system comprising a variable speed element, a source of supply connected with said element, a dynamo-electric machine supplied from said source and provided with substantig1 fiy-wheel effect so that its current varies with the rate of change of speed of said element, and a control device responsive to said current 5'. A control system comprising a variable speed element, means for producing a voltage substantially proportional to the speed or-said element,

element.

' machine and said supply means,

generator.

and a dynamo-electric machine energized from said voltage producing means and provided with substantial fly-wheel effect so that its current varies with the rated change oi! speed of said 6. A control system comprising a variable speed element, an electric motor, a pilot generator driven by said element, a dynamo-electric machine supplied from said generator and provided with substantial fly-wheeleflectso that its current varies with the rate of change of speed of said element, and means responsive to said cur- "rent for controlling said motor.

7. A control system for an electric motor comprising a variable speed element, a regulator for .unaintaining an operating characteristic 01 said motor substantially constant, means for producing a voltage varying with the speed of said element and a dynamo-electric machine energized ,from said voltage producing means, and provided so that its curwith substantial fly-wheel eflect rent varies with the rate of change of speed of said element, and means responsive to said current for controlling the action of said regulator.

8. A control system comprising a dynamo electric machine, supply means for said machine. a booster generator connected in circuit with said a variable voltage supply source and a dynamo-electric machine supplied' from said source and provided with substantial fly-wheel eilect for controlling said 9. A motor control system comprising an electric motor, a source of supply therefor, a booster generator connected in circuit with said motor and a dynamo-electric machine provided with substantial fly wheel effect and connected in the field circuit of said generator so as to control the voltagesupplied to said motor. 1

10. A'motor control system comprising a variable voltage source, a plurality from said source. a'boo'ster generator having its armature connected in circuit with the armature of one of said motors, means for supplying'a voltage varying with the speed of the other of saidof said machine to the "erator so that said generator controls said motor in accordance with variations in the current of said machine.

11. A system plurality oi! driving motbrsa regulator having an element responsive to the current of one oi said motors for maintaining the current input to said motor substantially constant, means responsiveto rate of change'oi! speed of theother of said motors for controlling the action of said regulator comprising a coil on said regulator for modifying the action of said current responsive of motor control comprising a 1 element, an auxiliary motor energized in accordfiice with the speed of said other motor, the armature of said auxiliary motor being connected to said (5611 and designed to haveily-wheel eflect, and a booster generator having its armature connected to said regulated motor and its field winding included in circuit with said coil and said auxiliary motor.

12. A control system iorapparatus having an element operating on a strip of material and a take-up reel for the delivered strip comprising a motor for driving said element, a motor for driving said reel, means for holding substantially constant tension in the, strip comprising a reguof motors supplied having substantial flywheel efiect and connections from the armature field circuit oi said gen-' lator having an operating element responsive to the current of said reel motor for maintaining substantially constant current input to said motor, means for varying the. setting said regulator to maintain the strip tension substantially constant during adjustments in the speeds or said motors comprising an auxiliary motor energized in accordan ce withthe speed of said element driving motor and designed with iiy-wheel v eiIect so as to draw change a currentvarying with the in speed of said element driving motor and a coil on said regulator for varying the action oi said current in circuit with said auxiliary for introducing avoltage in the responsive element connected motor, and means reel motor circuit varying' with the change in speed 01 said element driving motor. K

13. A control system for apparatus having an element operating on reel for the strip comprising a motor for driving a strip of-material and a said element, amotor connected. to said reel,

regulating means for said reel motor for maintaining the tension of said strip substantially constant, and means of said-regulating means substantially in proportion to rate of cha driving motor.

for modifying the operation nge of speed of said element 14. A control system ior apparatus operating a strip of material and a reel tor the strip comprising a motor motor connected to for said reel motor for maintaining for driving said element, a said reel, a current regulator the tension of said strip substantially constant, and means for varying the current setting of said regulator substantially in proportion to the acceleration and deceleration of v said element driving motor.

15. A control system for apparatus having an element operating on a strip of material and a reel for the strip, comprisinga motor for driving said element, a

motor connected tov said reel, 40

a regulator for controlling the operation or said reel motor, and control comprising a dynamo in accordance with said element driving means for said regulator electric machine controlle an operating condition of motor and an electroresponsive device connected in circuit with said dynamo electric machine for modifying the operation of said regulator.

16. A control system for apparatus having an element operating on a strip of material and a reel for the delivered strip comprising a motor for driving said element, a second motor for driv-- ing said reel, a regulator for maintaining the current input to said stant, an means rent to be held by dynamo electric for varying the value of ourmachine reel motor' substantially consaid regulator comprising a responsive to the rate oichange of speed of said element driving motor and an electroresponsive device connected in circuit with said machine ofsaid regulator.

1'7. A control system element operating on a strip reel iorthe strip comprising a ing said element, a a constant current for modifying the action for apparatus having an oi material and a motor for drivmotor connected to said reel, regulator for said reel motor v provided with a current responsive element, and means responsive to rate of change of speed of said element drivin rent setting or said regulator to maintain the strip g motor for varying the curtension substantially constant during speed changes comprising a dynamo electric machine equipped with an energy for supplying a voltage tional to the speed or said element driving motor,

storing device, means to said machine proporand a coil included in' circuit with said dynamo electric. machine for changing the action of said current responsive eleinen 18. A control system for apparatushaving an element operating on a strip of material and a reel for the strip comprising a motor for driving said reel, a motor for driving said element, a

constant current regulator for said reel motor reel motor current, current setting of said regulator 'in accordance with the acceleration of said element driving the strip tension substantially constant during speed changes comprising a pilot generator driven by said element driving motor, an auxiliary motor supplied from said generator and equipped with an energy storing fly-wheel, and a coil included in circuit with said auxiliary motor for varying. the action of said operating coil.

-19. A control system for 'mill apparatus and the like having motor driven rolls for operating on the strip and a reel for the strip, comprising to said reel, a regulator provided with a coil responsive to the reel motor curreel motor,

of said element driving motor for varying the'setting of said'regulator to maintain the'strip tension substantially constant during acceleration and deceleration comprising an auxiliary coil on said regulator connected across the armature of said elementdrivlng motor for varying the effect of said operating coil,

and, an auxiliary motor connected in the circuit provided with fly-wheel effect to provide for increasing the current in said auxiliary coil during acceleration and reduction of the auxiliary coil during deceleration. 21. A motor control system comprising a pincurrent in said responsive to the armature current of said auxiliary coil and rality of motors connected to a common load body, a regulator for maintaining the current input to one of said motors substantially constant, and means responsive to the rate of change of speed 01 the other or said motors for varying the setting of said regulator.

- 22. A control system for apparatus for winding and reelinga length of material having a reel for said material comprising a first dynamo electric machine mechanically connected tosaid reel,-a second dynamo electric machine mechanically connected to the material, at a point removed from said reel, a regulator for controlling said first machine to maintain the tension in the material substantially constant, and means responsive to the acceleration of said second machine for varying the settingof said regulator.

23. A control system comprising a plurality of dynamo electric machines connected to a strip of material, a regulator for maintaining the current flow in one 'of said machines substantially constant, and means responsive to the rate of change of speed of another of said machines for varying the setting of said regulator.

24. A control systemfor apparatus for winding and reeling a length of material having a reel for said material comprising in combination a first dynamo electric machine mechanically connected to said reel for tensioning the matesponsive to the rate of change of speed 01' said second machine for varying thesetting of said regulator to control said first machine .to maintain said tension substantially constant during acceleratii n and deceleration 01 said chine.

25. A control system for apparatus for winding and reeling a length of material having 'a reel and means for drawing said materiali'rom second masaid reel, 9. first-dynamo electric machine me chanically connected to said reel for tensioning said material, a second-dynamo electric machine a regulator for controlling the excitation of said first machine to maintain said tension substantially constant, said regulator-having a winding of said first machine, and a second winding, and means responsive to the rate of change of speed of said. second machinedor controllingthe energization of said second winding thereby to vary the.setting of said regulator so as to control said first machine to maintain' said tension substantially constant during acceleration and deceleration of said second machine.

A LeoNro A.

,mechanically connected to said drawing means, 

